Tags: Anatomical Structure, Embryology.
In early embryogenesis of most eutherian mammals the inner cell mass (abbreviated ICM and also known as the embryoblast or pluriblast the latter term being applicable to all mammals) is the mass of cells inside the primordial embryo that will eventually give rise to the definitive structures of the fetus. This structure forms in the earliest steps of development before implantation into the endometrium of the uterus has occurred.
